The present invention relates generally to a laser system that provides the elements for visually locating points of interest on a two-dimensional horizontal surface for use in primarily interior construction environments. A simple, accurate and cost effective system for the layout of floor plans at the jobsite has long been in need. Conventional GPS is not usable inside standard steel construction buildings. Previous laser based systems have been overly complex and expensive, missing the mark in almost every area required for this market.
In prior art laser based positioning systems, such as disclosed in U.S. Pat. No. 5,100,229, three or more laser transmitters (beacons) are placed around the perimeter of a work site. Each transmitter emits a plane of light approximately 45 degrees to vertical while continuously rotating at a constant speed. The beams from each transmitter must each have their own unique and highly controlled speed of rotation, or alternatively their own unique modulation frequency, so they may be distinguished from each other. A strobe on each provides a reference signal to start a series of timing events that are ultimately utilized to triangulate position. The system can be used for two-dimensional or three-dimensional applications. The complexity of this method is very high, and the requirement of having constant rotational laser scanning is critical. In addition, it is computationally intensive, especially when setting up the system.
Another prior apparatus, such as disclosed in U.S. Pat. No. 5,076,690, uses a rotating laser beam to scan retro-reflective bar coded targets placed around the perimeter of the job site. The portable transmitter/receiver utilizes optical collection optics to receive the retro-reflected energy from at least three of the targets. A rotational encoder assumes a relatively constant rotation speed and interpolates between each perimeter slot of the encoder disk a precision azimuth angle for each acquired target. After a set-up procedure that uses at least two known benchmarks, the working field is ‘scaled’ so that any other point of interest can be found with a two-dimensional working plane. A complex method to precision calibrate and characterize each leading edge of each rotary encoder slot is required to provide the level of precision sought in the construction layout application. Job site obstructions also become a challenge when acquiring sufficient targets in the right place, with respect to the position of the transmitter, to provide a strong calculation of position.
Still another method of laser based positioning is disclosed in U.S. Pat. No. 7,110,092. Two parallel laser beams are emitted at a known distance from each other. The beams are rotated together at a constant speed, thus defining the working plane. A laser receiver is used to determine when each beam becomes incident on the sensing element. Because the rotation of the beams is assumed to be constant, the timing of the two beams incident on the receiver becomes faster at greater distances and thus is a smaller percentage of the time it takes to traverse the entire perimeter. Distance is extrapolated from this information. Further, if an index is provided to indicate the start of rotation of the laser beams, then position can be found. Constant rotation speed is again very critical, and the position calculation for this method typically has not been sufficient accuracy for what is required for typical construction jobsite layout.
Still other laser based methods have been used to provide the construction layout function. Several of them, such as those manufactured and marketed by SL Laser, Leica, and Flexijet, utilize a pointing laser beam that is mounted on a rotating base that can provide azimuth angle and a frame with a rotatable sextant that can provide altitude angle. In this manner a laser beam can be pointed in the direction of a desired point of interest and projected onto a surface. The indicated point location is accurate only if the surface onto which it is projected is both flat and at the theoretically expected elevation. Otherwise serious errors can occur, and become increasingly large as the incident projection angle onto the surface becomes steeper.
It is seen that there remains a need for a more effective positioning system for use in the construction industry and, more specifically, for floor layout indoors. This need encompasses the desire for more simplicity so that its concept of operation and method of use is much more intuitive to the user. Set up of the system should be straightforward and fast. In addition, there is a need to provide a visual system for interior use. Doing so will add to the intuitive nature of the system as well as reduce the overall expense of the system, because the function of automatically detecting an encoded or modulated laser signal is not required. Lastly, there is a need to provide a system where the projection onto a surface is not subject to flatness errors of the incident surface.